Image forming device

ABSTRACT

An image forming apparatus has a feature in a sheet ejecting section thereof. With a simplified configuration, the image forming apparatus ensures that a tail end of a sheet is prevented from being lifted up at an image forming position.  
     The image forming apparatus has sheet ejecting rollers ( 4 ) arranged below a sheet transport path. The apparatus also has sheet pinch rollers ( 8 ), a first lift-preventing roller ( 1 ), and a second lift-preventing roller ( 16 ) arranged above the sheet transport path. The rollers ( 8 ), the roller ( 1 ), and the roller ( 16 ) are in direct contact with the rollers ( 4 ) at respective points in the sheet transport direction.

TECHNICAL FIELD

The invention relates to an image forming apparatus which performs aprocess of forming an image on a sheet of paper, and in particular to animage forming apparatus having a feature in a sheet ejecting sectionthereof.

BACKGROUND

Image forming apparatus such as ink jet printers have a sheet transportpath leading from a sheet feeding section through an image formingposition to a sheet ejecting section. A sheet is transported along thesheet transport path to the sheet ejecting section, to be ejected fromthe image forming apparatus onto a sheet receiving tray provided in thevicinity of the sheet ejecting section. Sequential guidance of sheetswith images formed thereon to the receiving tray allows a user to pickup the sheets smoothly.

As more and more sheets are accumulated on the receiving tray, however,the sheets may sometimes block the sheet ejecting section. Morespecifically, a large number of sheets accumulated on the receiving traysometimes become an obstacle to smooth ejection of subsequent sheetsfrom the image forming apparatus.

In view of the foregoing, conventional image forming apparatus have asheet receiving tray provided at a position lower than that of a sheetejecting section, thereby preventing sheets accumulated on the receivingtray from blocking the sheet ejecting section.

FIG. 1 illustrates a schematic construction of an ink jet printer 100 asa typical example of a conventional image forming apparatus. As shown inFIG. 1, the ink jet printer 100 has a sheet receiving tray 107 providedat a position lower by height H than that of a sheet ejecting section.Note that the height H is here set to 20 mm or more so that 150 or moresheets P can be stacked on the receiving tray 107.

The conventional image forming apparatus as illustrated in FIG. 1 has asheet transport path leading from a sheet feeding section through animage forming position to the sheet ejecting section. A sheet P to betransported along the sheet transport path is nipped between a platenroller 103 and a sheet holding roller 105, which are both arranged alongthe sheet transport path, so that the sheet P is guided downstream in asheet transport direction.

A printhead section 112 and a lower sheet guide 114 are also providedalong the sheet transport path, downstream of the platen roller 103 andthe sheet holding roller 105. The image forming position is provided ina space between the printhead section 112 and the lower sheet guide 114.A sheet ejecting roller 104 and a sheet pinch roller 108 are arrangeddownstream of the image forming position in the transport direction.

As described above, the ink jet printer 100 has the sheet receiving tray107 provided at a position lower by height H than that of the sheetejecting section. Accordingly, a large number of sheets accumulated onthe receiving tray do not block the sheet ejecting section.

Such conventional image forming apparatus as described above isdisclosed by JP H06-071956 A, JP 2001-302054 A, and JP2002-113913 A.

[Problem to be Solved]

Because the sheet receiving tray 107 is provided at the position lowerby height H than that of the sheet ejecting section, however, a tail endof the sheet P to be ejected may sometimes become in contact with theprinthead section 112. This causes a new problem of improper imageformation, as discussed below.

At the beginning of an image forming process, the tail end of the sheetP is nipped between the platen roller 103 and the sheet holding roller105. As the sheet P is transported downstream in the sheet transportdirection, the tail end passes through the nip area of the platen roller103 and the sheet holding roller 105. At the end of the image formingprocess, the sheet P to be ejected from the ink jet printer 100 isnipped between the sheet ejecting roller 104 and the sheet pinch roller108.

Accordingly, at the end of the image forming process, a leading end ofthe sheet P may sometimes hang down under its own weight, so that thetail end is lifted up, as illustrated in FIG. 1. Thus, the tail end isthus elevated above a reference level and a print surface of the sheet Pbecomes in contact with an ink discharging surface of the printheadsection 112, so that the sheet P is contaminated with ink.

Conventional solutions to the new problem have been: a sheet receivingtray which slopes upward to a free end thereof; the sheet pinch rollers108 which are fixedly mounted and arranged in two lines at a downstreamposition of the printhead section 112; and the like. However, suchconventional solutions cause the ink jet printer 100 to be enlarged.Also, such conventional solutions require the sheet pinch rollers 108 tobe mounted with high precision.

A feature of the present invention is to offer an image formingapparatus with a simplified configuration ensuring that a tail end ofsheet is prevented from being lifted up in an image forming position.

DISCLOSURE OF THE INVENTION

(1) An image forming apparatus of the invention includes: a sheettransport path leading from a sheet feeding section through an imageforming position to a sheet ejecting section;

a lower sheet ejecting roller arranged in the sheet ejecting sectionbelow the sheet transport path; and

an upper sheet ejecting roller arranged above the sheet transport pathso as to be in direct contact with the lower sheet ejecting roller,

wherein the upper sheet ejecting roller is divided in a directionperpendicular to a sheet transport direction into a plurality ofportions and is in direct contact with the lower sheet ejecting rollerat respective points in the sheet transport direction.

In the image forming apparatus as thus configured, the lower sheetejecting roller and the upper sheet ejecting roller are provided in thesheet ejecting section. The sheet ejecting section is located mostdownstream along the sheet transport path and serves to eject a sheetout of the apparatus.

The upper sheet ejecting roller is divided in the directionperpendicular to the sheet transport direction into the plurality ofportions. The portions are in direct contact with the lower sheetejecting roller at a plurality of points in the sheet transportdirection. The upper sheet ejecting roller as typically configuredincludes a plurality of supports which are arranged at differentpositions in the sheet transport direction, and component parts whichare rotatably supported by the supports.

A sheet to be ejected out of the image forming apparatus is nipped atdifferent points in the sheet transport direction between the uppersheet ejecting roller and the lower sheet ejecting roller. Thus, thesheet as thus nipped between the upper and lower sheet ejecting rollersis less likely to be turned than a sheet which is nipped at a singlepoint between the upper and lower sheet ejecting rollers.

Accordingly, even when a leading end of a sheet being transported hangsdown with its own weight, a tail end thereof is prevented from beinglifted up, so that the tail end is prevented from becoming in contactwith a printhead section.

Also, the sheet is allowed to keep level while passing through the imageforming position. This allows a constant distance to be maintainedbetween the sheet and the printhead section. Thus, a simplifiedconfiguration enables proper sheet transport.

(2) Part or all of the portions of the upper sheet ejecting roller aredisplaced from one another upstream or downstream in the sheet transportdirection.

In the image forming apparatus as thus configured, the portions intowhich the upper sheet ejecting roller is divided are displaced from oneanother upstream or downstream in the sheet transport direction. Theupper sheet ejecting roller is thus in direct contact with the lowersheet ejecting roller at a plurality of points in the sheet transportdirection.

Accordingly, when a leading end of a sheet to be ejected out of theapparatus hangs down with its own weight, a tail end of the sheet isprevented from being lifted up.

(3) The upper sheet ejecting roller includes a sheet pinch roller, afirst lift-preventing roller, and a second lift-preventing roller. Thesheet pinch roller, the first lift-preventing roller, and the secondlift-preventing roller are in direct contact with the lower sheetejecting roller at respective points in the sheet transport direction.

In the image forming apparatus as thus configured, the upper sheetejecting roller includes the sheet pinch roller, the firstlift-preventing roller, and the second lift-preventing roller, all beingprovided at different positions in the sheet transport direction. Thesheet pinch roller is positioned on the lower sheet ejecting roller, andthe first and second lift-preventing rollers are positioned upstream anddownstream, respectively, in the sheet transport direction of the sheetpinch roller.

Accordingly, even when a leading end of a sheet to be ejected onto asheet receiving tray hangs down with its own weight, the firstlift-preventing roller positioned upstream of the sheet pinch rollerprevents a tail end of the sheet from being lifted up. Further, thesecond lift-preventing roller serves to guide the leading end smoothlyto the sheet receiving tray which is provided below the sheet ejectingsection. Furthermore, need is eliminated for a plurality of upper sheetejecting rollers. The image forming apparatus thus can have a simplifiedconfiguration.

(4) The sheet pinch roller, the first lift-preventing roller, and thesecond lift-preventing roller are arranged symmetrically in relation toa center line of the sheet transport path.

In the image forming apparatus as configured above, the sheet pinchroller, the first lift-preventing roller, and the second lift-preventingroller are symmetrically arranged in relation to the center line of thesheet transport path. The center line of the sheet transport path hereinis a line which is parallel to the sheet transport direction and passesthrough the center of the sheet transport path.

Accordingly, a sheet passing between the upper and lower sheet ejectingrollers is prevented from being skewed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a schematic construction of aconventional image forming apparatus;

FIGS. 2(A) and 2(B) are diagrams illustrating a schematic constructionof an ink jet printer of the invention;

FIG. 3 is a plan view illustrating a schematic construction of the inkjet printer; and

FIG. 4 is a block diagram illustrating a schematic construction of theink jet printer.

THE BEST MODE FOR CARRYING OUT THE INVENTION

With reference to the drawings, described below is an ink jet printer 20according to an embodiment of the invention. Note that recording paper,a sheet material, ink jet printing paper, and the like are hereincollectively referred to as a sheet.

FIG. 2(A) is a diagram illustrating a schematic construction of the inkjet printer according to the embodiment. The ink jet printer 20 isprovided with a sheet feeding tray 9 as a sheet feeding section. In thesheet feeding tray 9, sheets to undergo image forming processes arestored. A sheet transport path leads from the tray 9 through an imageforming position to be described later, to a sheet ejecting section.

Arranged in the vicinity of the tray 9 is a sheet separating section 6and a sheet feeding roller 10. The sheet separating section 6 picks up atop sheet P and the sheet feeding roller 10 feeds the sheet P into thesheet transport path. Arranged downstream of the tray 9 in a sheettransport direction is a sheet detecting sensor 13 for detecting passageof the sheet P.

A platen roller 3 and sheet holding rollers 5 are provided downstream ofthe sensor 13 along the sheet transport path. The platen roller 3 andthe sheet holding rollers 5 are positioned on opposite sides of thesheet transport path, so as to be in direct contact with each other. Therollers 5 are rotatably supported by a roller holder 2.

Downstream of the platen roller 3 and the sheet holding rollers 5 in thesheet transport direction, a printhead section 12 and a lower sheetguide 14 are arranged on opposite sides of the sheet transport path. Theprinthead section 12 has an ink cartridge, and nozzles for dischargingink. The lower sheet guide 14 is provided below the printhead section 12so that the sheet P is kept level while being transported. The imageforming position of the invention is provided in a space between theprinthead section 12 and the lower sheet guide 14.

Arranged downstream of the image forming position along the sheettransport path are sheet ejecting rollers 4 and sheet pinch rollers 8.The sheet ejecting rollers 4 and the sheet pinch rollers 8 arepositioned on opposite sides of the sheet transport path, so as to be indirect contact with each other.

Conventionally, the rollers 4 and the rollers 8 are paired to form thesheet ejecting section. In the case, after a tail end of the sheet Ppasses between the platen roller 3 and the sheet holding rollers 5, aleading end thereof hangs down with its own weight. The sheet P isturned around nip areas of the sheet ejecting rollers 4 and the sheetpinch rollers 8, so that the tail end of the sheet P is inconvenientlylifted up to come in contact with the printhead section 12.

In view of the foregoing, the ink jet printer 20 of the presentembodiment has first lift-preventing rollers 1 and a secondlift-preventing roller 16. The rollers 1 and the roller 16 are arrangedupstream and downstream, respectively, of the sheet pinch rollers 8along the sheet transport path, so as to be in direct contact with thesheet ejecting rollers 4. The upper sheet ejecting roller of theinvention includes the sheet pinch rollers 8 for pressing the sheet Pagainst the sheet ejecting rollers 4, the first lift-preventing rollers1 which are arranged upstream of the rollers 8 in the sheet transportdirection, and the second lift-preventing roller 16 which is arrangeddownstream of the rollers 8.

FIG. 2(B) illustrates a configuration of the components in the vicinityof the sheet ejecting rollers 4. Described below are respectivematerials and sizes of the above-discussed rollers in the presentembodiment. The sheet ejecting rollers 4 are made of EPDM rubber andhave a diameter of 12.0 mm. The sheet pinch rollers 8, the firstlift-preventing rollers 1, and the second lift-preventing roller 16 aremade of stainless steel (SUS304CSP) and have a diameter of 9.2 mm.

A sheet receiving tray 7 is provided at a position where the sheet P isejected after passing through the sheet ejecting section which includesthe sheet ejecting rollers 4, the sheet pinch rollers 8, the firstlift-preventing rollers 1, and the second lift-preventing roller 16. Thesheet receiving tray 7 is arranged at a position lower by 20 mm thanthat of the second lift-preventing roller 16.

FIG. 3 is a plan view illustrating a schematic construction of the inkjet printer 20. Note that the sheet transport direction is a downwarddirection on the sheet of FIG. 3 and that a main scanning direction is ahorizontal direction on the same. Also note that in the figure an arrowW points to a standby position of the printhead section 12 and an arrowH points to a home position of the same. Further, a range indicated byan arrow A is a print area.

As illustrated in FIG. 3, the first lift-preventing rollers 1 areattached to a sheet pinch roller guide 15. The first lift-preventingrollers 1 are constantly biased elastically toward the sheet ejectingrollers 4. A typical example of a biasing device for the rollers 1 is aspring for applying a force toward the roller 4 to the rollers 1.

The second lift-preventing roller 16 and the sheet pinch rollers 8 arealso attached to the guide 15 and are constantly biased toward therollers 4.

FIG. 4 is a block diagram illustrating a schematic configuration of acontrol system of the ink jet printer 20. As illustrated in FIG. 4, theink jet printer 20 has a control board 50, a sub board 51, a sheet feedmotor system 52, a carrier motor system 53, a maintenance motor system54, a cam switch 55, the sheet detecting sensor 13, and the printheadsection 12.

The sheet feed motor system 52 is used for transporting the sheet P. Thecarrier motor system 53 is used for moving the printhead section 12. Themaintenance motor system 54 is used for maintenance operations such ascleaning of the printhead section 12. The cam switch 55 is used forswitching power supply among the components of the ink jet printer 20,including the systems 52, 53, and 54. The sub board 51 controlsoperations of the respective components of the ink jet printer 20according to a signal from the control board 50. The control board 50 isused for data communication between the printer 20 and an external PCand for analysis of operational information input through operation keysby an user.

In the ink jet printer 20, a top sheet of paper P stacked in the sheetfeeding tray 9 is picked up by the sheet separating section 6 and thenfed into the sheet transport path. The sheet P is transported to such aposition as to turn on the sheet detecting sensor 13.

The sheet P is transported a predetermined distance until the sheet Pcomes in contact with the platen roller 3. Then, the sheet P is halted.At the time, the sheet feeding roller 10 is deactivated and the platenroller 3 is activated instead. The sheet P is transported in between theplaten roller 3 and the sheet holding rollers 5 and then transported toa position which is approximately 1.0 to 1.5 mm upstream, in the sheettransport direction, of an ink discharge position of the printheadsection 12. At the time, the sheet ejecting rollers 4 are alsoactivated.

A leading end of the sheet P is transported to a print start positionbefore the transport of the sheet P is halted. While traveling in themain scanning direction which is perpendicular to the sheet transportdirection, the printhead section 12 discharges a jet of ink according toprint data input to the control board 50. After traveling along a linefor printing, the printhead section 12 returns to the standby positionas pointed to by the arrow W in FIG. 3. Then, the platen roller 3 sendsthe sheet P exactly one line forward in the sheet transport direction,i.e., in a sub scanning direction. In the same manner, the printheadsection 12 travels along subsequent lines for printing.

The sheet P is transported in the sheet transport direction, one line ata time, by the platen roller 3. After a leading end of the sheet Preaches the sheet ejecting rollers 4, the sheet P is transported in thesheet transport direction by the platen roller 3 and the rollers 4.While being transported downstream along the sheet transport path, thesheet P undergoes a printing process according to the print data. Theprinting process still continues after the sheet P proceeds with a tailend past the sheet detecting sensor 13 and therefore is no longerdetectable by the sensor 13. As the printing process further proceeds,the tail end of the sheet P moves away from the platen roller 3. Then,the sheet P is transported by the sheet ejecting rollers 4 whileundergoing the printing process to the tail end.

Even after the tail end passes through the platen roller 3 and the sheetholding rollers 5, the tail end is nipped between the firstlift-preventing rollers 1 and the sheet ejecting rollers 4, and is thusprevented from being lifted up. Accordingly, the tail end proceeds alongthe lower sheet guide 14, so that the sheet P properly undergoes theprinting process to the tail end.

The sheet pinch rollers 8 are positioned nearer the center of the sheetP in relation to the first lift-preventing rollers 1 positioned at bothside portions of the sheet P, so that any one of the rollers 8 and anyone of the rollers 1 are not on the same straight line parallel to thesheet transport direction. A reduced mutual interference with transportspeeds of the rollers 8 and the rollers 1 allows smooth transport of thesheet P. The second lift-preventing roller 16 is positionedapproximately 4 mm downstream of the rollers 8, thereby allowing thesheet P to be ejected downwards.

Any one of the first lift-preventing rollers 1, the secondlift-preventing roller 16, and any one of the sheet pinch rollers 8 arenot in the same straight line parallel to the sheet transport direction.Accordingly, there is a reduced mutual interference with transportspeeds of the rollers 1, the roller 16, and the rollers 8.

The sheet P is transported from upwards to downwards in the sheet ofFIG. 3. In the present embodiment, the first lift-preventing rollers 1,the sheet pinch rollers 8, and the second lift-preventing roller 16,i.e., seven rollers in total, are evenly spaced in a directionperpendicular to the sheet transport direction. The secondlift-preventing roller 16 are positioned at the center of the sevenrollers. On either side of the roller 16, the first lift-preventingroller 1, the sheet pinch roller 8, and again the first lift-preventingroller 1 are arranged in the mentioned order. Specifically, the rollers1 and the rollers 8 are arranged symmetrically with the roller 16 as asymmetry center.

After passing through the image forming position, the leading end of thesheet P first comes in contact with the first lift-preventing rollers 1.The rollers 1 outnumber the other rollers in the direction perpendicularto the sheet transport direction. Accordingly, the leading end isunlikely to get jammed in nip areas of the sheet ejecting rollers 4 andthe rollers 1, so that the sheet P is transported smoothly. Also, in thedirection perpendicular to the sheet transport direction, the firstlift-preventing rollers 1, the sheet pinch rollers 8, and the secondlift-preventing roller 16 are arranged symmetrically in relation to acenter line of the sheet transport path. The sheet P is thus preventedfrom being skewed while being transported.

In the present embodiment, the first lift-preventing rollers 1, thesheet pinch rollers 8, and the second lift-preventing roller 16, i.e.,seven rollers in total, are evenly spaced in the direction perpendicularto the sheet transport direction. However, arrangement of the rollers isnot to be considered to be limited to the foregoing one.

In the image forming apparatus as configured above, the tail end of thesheet P is prevented from being lifted up after passing through theplaten roller 3. Thus, the tail end neither comes in contact with theprinthead section 12 nor gets caught in sheet transport rollers. Thisleads to solving problems such as of the sheet P being contaminated withink or being damaged. Also, there is allowed a reduced mutualinterference with transport speeds of the sheet ejecting rollers 4, thefirst lift-preventing rollers 1, and the second lift-preventing roller16. Therefore, the sheet P undergoes a proper printing process from theleading end to the tail end.

The first lift-preventing rollers 1, four in total, are attached to thesheet pinch roller guide 15 so as to be positioned preferablyapproximately 4 mm upstream of the sheet pinch rollers 8 along the sheettransport path. The positioning allows the sheet P to be pressed evenlyby the first lift-preventing rollers 1 and the sheet ejecting rollers 4even after the tail end of the sheet P passes through the sheet holdingrollers 5. The tail end is thus prevented from being lifted up, and isthus transported along the lower sheet guide 14. Accordingly, it ispossible to solve the problems such as of the sheet P being contaminatedwith ink or being damaged.

Also, the second lift-preventing roller 16 is positioned approximately 4mm downstream of the sheet pinch rollers 8, so that the leading end ofthe sheet P is turned downward. This allows the sheet P to be smoothlyguided to the sheet receiving tray 7.

Note that the sheet pinch rollers 8 and the second lift-preventingroller 16 may sometimes have different transport speeds depending onslight variations in size of component parts thereof. Therefore, whenthe rollers 8 and the roller 16 are arranged in the same line parallelto the sheet transport direction, there may be caused a mutualinterference with transport speeds of the rollers 8 and the roller 16,so that the sheet P is prevented from being transported smoothly and iseven skewed.

In the present embodiment, however, each of the sheet pinch rollers 8are arranged between one pair of the first lift-preventing rollers 1,with a reduced mutual interference with the transport speeds. Further,the second lift-preventing roller 16 are arranged between the sheetpinch rollers 8, with a reduced mutual interference with the transportspeeds. Accordingly, the sheet P being transported is prevented frombeing skewed.

1) An image forming apparatus, comprising: a sheet transport pathleading from a sheet feeding section through an image forming positionto a sheet ejecting section; a lower sheet ejecting roller arranged inthe sheet ejecting section below the sheet transport path; and an uppersheet ejecting roller arranged above the sheet transport path so as tobe in direct contact with the lower sheet ejecting roller, wherein theupper sheet ejecting roller is divided in a direction perpendicular to asheet transport direction into a plurality of portions and the portionsare in direct contact with the lower sheet ejecting roller at respectivepoints in the sheet transport direction. 2) An image forming apparatusaccording to claim 1, wherein part or all of the portions of the uppersheet ejecting roller are displaced from one another upstream ordownstream in the sheet transport direction. 3) An image formingapparatus according to claim 1, wherein the upper sheet ejecting rollerincludes a sheet pinch roller, a first lift-preventing roller, and asecond lift-preventing roller, and wherein the sheet pinch roller, thefirst lift-preventing roller, and the second lift-preventing roller arein direct contact with the lower sheet ejecting roller at respectivepoints in the sheet transport direction. 4) An image forming apparatusaccording to claim 3, wherein the sheet pinch roller, the firstlift-preventing roller, and the second lift-preventing roller arearranged symmetrically in relation to a center line of the sheettransport path.